Science FairQuestionIf two noises are played that are totally out of phase, will they cancel each other out?

HypothesisIt is possible to cancel out some of the noise, but not all of it.

Theory

Noise cancellation is a very interesting procedure. First, an initial sound wave is emitted from one source. Next, a sound wave with the same amplitude and frequency, but totally out of phase is emitted from a second source. When this second wave is combined with the first wave, destructive interference occurs (see figure 1), and the sounds cancel each other out.

Materials• PC computer• 2 speakers• Audacity application

Procedure

1. Visit the website Sine Tone Generator (http://www.audiocheck.net/audiofrequencysignalgenerator_sinetone.php)

2. Download a .wav file with a frequency of 1000Hz.3. Open the file in the Audacity application.4. In Audacity:

a. Split the stereo sound to a mono sound. [Split stereo to mono]b. Make each sound emit from a different speaker. [Left channel and right channel]c. Invert one of the sounds. [Effect > Invert]d. Repeat both 3 second sounds nine times so they each last 30 seconds. [Effect

> Repeat]5. Connect two speakers to the computer.6. Play the sound file on Audacity, modifying the placement of the speakers, and powering

one or both of the speakers.

Facts

Noise-canceling headphones can reduce the amount of ambient low-frequency noise heard on airplanes by 20 decibels.

Active noise control is used in headphones to cancel lower-frequency noise. This contrasts with passive noise control, such as soundproofing, which is used to prevent higher-frequency noise from reaching the ears.

ObservationsFour scenarios with the same settings produced different results.

1. Two speakers; two meters apart: Both speakers are heard, equivalent to the volume of sound from one speaker.

2. One speaker powered on, two meters from another which is powered off: Only the powered speaker could be heard, with the volume of sound identical to that of both speakers on.

3. Two speakers; two meters apart to zero centimeters apart: As the speakers were brought closer, the volume of sound began to decrease, until it was negligible.

4. One speaker powered on, zero centimeters from another which is powered off: The volume of sound is equal to the volume of sound in the first two scenarios.

Conclusion

In conclusion, if two sounds of opposite phase are played next to each other, destructive interference occurs. The experiment was much more conclusive than expected, and an appreciable difference was heard. The experiment was a success!

Bibliography

https://www.val.me.vt.edu/research/activenoisecontrol

http://en.wikipedia.org/wiki/Noise-cancelling_headphones

http://en.wikipedia.org/wiki/Active_noise_control

https://answers.yahoo.com/question/index?qid=20100508000504AAzqpOo

http://electronics.howstuffworks.com/gadgets/audio-music/noise-canceling-headphone3.htm

https://www.youtube.com/watch?v=YNK4Wc3-Ij4

http://www.audiocheck.net/audiofrequencysignalgenerator_sinetone.php

https://journalxtra.com/easyguides/how-to-make-a-semi-transparent-image-using-gimp/